If an operating device is isolated from the mains voltage, these capacitors retain their voltage for a certain period of time, and there is therefore the risk of electric shock for a user, for example an electrician, when coming into contact with the mains terminals on the operating device. In some countries there is therefore a regulation which prescribes that the voltage at the mains terminals on the operating device needs to be lowered to an unhazardous voltage within a short period of time.
In order to adhere to this regulation, two different approaches are provided in the prior art. One approach consists in selecting the X capacitors to have such a low value that, with the low current consumption in the standby mode of the device, i.e. when the lamps are switched off, these capacitors are discharged in the prescribed time.
The other possibility consists in increasing the intrinsically low standby consumption of a modern electronic operating device artificially in order to discharge the capacitors in the prescribed time.
However, both embodiments have disadvantages. If the capacitors are selected so as to have too low a value, they are no longer capable of performing their actual task of filtering out mains faults and high-voltage pulses. The consequence of this is failures of the electronic operating devices owing to overvoltages in the power supply system. It is also possible under certain circumstances for faults caused by the electronic operating device to no longer be sufficiently filtered, with the result that applicable EMC (electromagnetic compatibility) regulations can no longer be adhered to.
If the capacitors are selected to have a sufficiently high value, the intrinsically very low current consumption of the operating device in the standby mode needs to be artificially increased, which has a negative effect on the total current consumption and ultimately also on the environment.
An additional problem has proven to be another backup capacitor downstream of the rectifier, which is provided in a very large number of operating devices and is intended to smooth the rectified AC voltage. In order to perform this task, the capacitor is dimensioned so as to have a very high value. Since it is connected in parallel with the X capacitors via the rectifier it must be discharged by the standby consumption at the same time as the X capacitors in order to be able to adhere to the prescribed standard.